The invention relates to a crankshaft drive of an internal-combustion engine of V-type which has two mutually offset crank pins per throw between pairs of crankshaft webs.
A crankshaft is known, inter alia, from German Published Unexamined Patent Application (DOS) No. 2,341,082, in which offset crank pins are interconnected via an intermediate element. However, this German application does not mention anything regarding the axial guidance of two connecting rods mounted on these crank pins.
In the case of a crankshaft drive disclosed by German Published Unexamined Patent Application (DOS) No. 3,541,903 for the attainment of a predetermined timing interval, the crank pins are arranged offset within a throw and are interconnected via a non-bearing intermediate web. In this arrangement, the intermediate web is also used as the axial guidance of both connecting rods, whereby, in contrast to throws with continuous connecting rods otherwise conventional in V-type engines, the connecting rods are also subjected on the mutually facing inner sides to a fully rotational axial contact movement, entailing increased frictional losses, with respect to the intermediate web. It is furthermore known from the U.S. Pat. No. 2,780,502 to guide two connecting rods mounted on a common crank pin axially opposite via correspondingly designed bearing shells.
Reference is also made to co-pending commonly assigned application Ser. No. 234,919, based on German Application P No. 37 28 013.9, filed in Germany on Aug. 22, 1987.
An object of the present invention is to provide a crankshaft drive of the type referred to above which reduces, as far as possible, the frictional losses caused by the axial contact of the contacting rods while at the same time retaining optimum guidance of both connecting rods.
This object is achieved according to the invention by providing an arrangement wherein each connecting rod is guided on a second side by means of an axial stop surface arranged on the connecting rod eye of an adjacent connecting rod. The width of each connecting rod eye is greater than the width of the associated crank pin in the guidance region. Further, the axial stop surfaces are so large that in every crankshaft position there is a cohesive overlapping of the two manually guided axial stop surfaces of the connecting rods.
The design of the crankshaft drive according to the invention has the effect that the two connecting rods guide each other, despite the crank pin offset. Specifically, the guidance of the connecting rods is facilitated by the two axial stop surfaces being arranged on the large connecting rod eyes, which have the axial stop surfaces formed on the outer contour so that in every crankshaft position a cohesive overlapping area of the contacts is ensured. Since each of the two connecting rod eyes is wider than the associated crank pin, the guidance plane lies at the level of the intermediate element, so that it is impossible for a protruding connecting rod eye to run on to the adjacent crank pin.
Moreover, in the case of a crankshaft drive of this design, the friction pairing of the stop surfaces is only subjected to the relative movement of the connecting rods relative to one another, which, owing to the V-shaped cylinder arrangement, consists of a reciprocating angular movement and, because of the crank of the crank pin offset, of a local translatory displacement. This results in lesser hydrodynamic losses than in the case of a full rotary contact movement of the connecting rods with double friction pairing, as is the case when an intermediate web is used.
Owing to the intermediate element, which connects the two crank pins to one another and has a cross-sectional which corresponds to the sectional area of the overlapping cross-section of two crank pins, undesired radii intersections are omitted here, so that the crankshaft is simple to produce and overly high notch stresses are avoided.
In preferred embodiments of the crankshaft drive a further saving regarding friction is obtained by an arrangement wherein, even with offset crank pins, the bearing covers are designed to be narrower that the connecting rods in the region of the large connecting rod eyes, so that they do not participate in the axial guidance and do not need to be micro-finished at the sides. With the reduction of the friction surfaces, the hydrodynamic loss, which is now only obtained from the rod-sided overlapping, is also reduced here.
An overlapping of the two axial stop surfaces in every crankshaft position, which is still cohesive despite the choice of a larger crank pin offset, is obtained in preferred embodiments of the crankshaft drive. Further, the mutual guidance of the two connecting rods is effected only via the axial stop surfaces of the bearing rod shank-sided part of the connecting rod eyes and therefore, the bearing covers are together reduced in width by the amount, to be calculated from the weight, by which the connecting rods have increased, in terms of weight, due to the radial enlargement of the axial stop surfaces. Since the bearing covers do not participate in the axial guidance, the rotating mass increase, caused by the widening of the stop surfaces arranged on the rod side, can be compensated without problem by a corresponding reduction of the bearing cover width, without the unnecessarily increasing the mass of the crankshaft drive.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.